1. Field of the Invention
The present invention relates to a drive transmitting mechanism in which a driving shaft and a driven shaft are arranged in a axial alignment and can be coupled and decoupled, and a rotational drive force is transmitted from the driving shaft to the driven shaft via a pair of coupling members, and to an image forming apparatus that comprises this drive transmitting mechanism.
2. Description of the Related Art
In laser printers and digital copiers, which are designed to print high-quality images, the change in the rotational speed of the photosensitive drum greatly influences the image quality. Therefore, the structure of the drive coupling unit for rotating the photosensitive drum is an important element in designing the structure of the copier.
In a color copier of so-called quadruple-tandem type, and the like, the rotational speed change of the photosensitive drum per rotation results from the de-centering and declination between the rotating shaft of the photosensitive drum and the driving shaft that rotates the drum. This rotational speed change results in color misalignment on the printed sheets.
A method of minimizing the de-centering and declination between the rotating shaft of the photosensitive drum and the driving shaft is known. In this method, the driving shaft is fitted in the drum, thus positioning the driving shaft. This method is disadvantageous, however, in that the position adjustment of the driving shaft with respect to the shaft of the drum is extremely difficult to achieve. Copiers and the like comprise many driven components. Hence, even if the driving shaft is precisely positioned with respect to the rotating shaft of the drum, it is anticipated that the vibration caused by these driven components generate the misalignment between the rotating shaft and the driving shaft as time passes, due to. Every time misalignment develops between the rotating shaft and the driving shaft, the rotating shaft and the driving shaft must be positioned again with respect to each other.
The Oldam coupling is known as a coupling mechanism that couples a driving shaft and a driven shaft so that a driving force may be transmitted from the driving shaft to the driven shaft. The Oldam coupling can indeed compensate for (absorb) the de-centering, but cannot compensate for the declination. It is therefore necessary to increase the degree of parallelism between the driving shaft and the driven shaft.
JP2002-48148 discloses a driving-force transmitting device comprising a coupling that has amount of freedom (can move) in the radial direction and thrust direction. The coupling is configured to compensate for de-centering and declination at the same time. The coupling is attached to either the driving shaft or the driven shaft.
In this driving-force transmitting device, however, only one of the shafts responds to de-centering and declination. A large load is inevitably applied to that part of the coupling to which this shaft is attached. The load is so large that the coupling may be deformed or may be broken.
For the maintenance of any image forming apparatus, the photosensitive drum is cleaned or replaced by a new one. In such case, the photosensitive drum is pulled from the housing of the image forming apparatus. After cleaned, the photosensitive drum is set back in the housing. Otherwise, a new drum is set in the housing. In this case where the coupling disclosed in JP2002-48148 may be used to rotate the photosensitive drum, the efficiency of connecting this coupling to the photosensitive drum to set the drum in the housing of the image forming apparatus is not high.